1. Field of the Invention
The present invention relates generally to wind turbines used for generating electricity, and more particularly, to wind turbine towers modified for storing hydrogen and, in some embodiments, for storing energy for later use or transmittal over the grid.
2. Relevant Background
Around the world, there is an increasing demand for satisfying energy requirements in ways that use less or no fossil fuels. These alternatives need to be reliable, cost effective, and environmentally sound to be adopted on a large scale. For example, as the need to stabilize energy resources increases, many nations and electric utilities are evaluating the increased use of wind as a portion of their power generation mix. Additionally, the use of hydrogen as a “clean” fuel to replace fossil fuels is being seriously considered and investigated by many in the energy industry.
The terms “wind energy” and “wind power” describe the process by which wind is used to generate electricity. Wind turbines convert the kinetic energy in the wind into mechanical power through the use of a rotor that spins a shaft. The shaft is connected to a generator that converts the mechanical power into electricity. The electricity is typically transmitted from the generator to a utility grid for further distribution. The rotor attaches to a hub or nacelle that also houses the generator. The nacelle sits atop a tower, such as a tubular steel or concrete tower or a lattice tower. An ongoing trend is to use taller and taller towers (i.e., 50 to 100 meters or more) because wind speed typically increases with height and more electricity can be generated with the taller towers. The tower not only positions and vertically supports the nacelle and attached rotor but is designed to withstand the strong bending forces created by the rotor.
Wind energy is currently the most cost effective, non-hydro, renewable energy source, but a number of issues need to be addressed before it will be more widely adopted by nations and utilities. Wind energy is intermittent and is only available when the wind is blowing within a particular range of wind speeds, i.e., the turbine cannot operate at wind speeds below a minimum speed and cannot be safely operated above a maximum speed. Hence, the energy from the wind turbine is only available intermittently. Further, wind power is seasonal in many areas of the world with stronger winds occurring in one season or another depending on the location. Another issue with wind energy is that wind energy is inherently not dispatchable because the output of wind farms, i.e., collections of wind turbines, is a function of wind speed, and the utilities cannot control wind speed. Dispatchability refers to the ability to control output, and this is important because energy users and not the utility control the load on a grid. Hence, the utilities must control power injected into the grid by power generators (such as wind farms) to set it equal to the power withdrawn from the grid by end users. Since wind power does not presently lend itself to control, utilities must include other more dispatchable sources of energy. Another issue with adopting wind energy is cost. Other sources of energy are consistently less expensive for providing electricity to a utility grid, and wind energy is often only included in a grid when its use is subsidized by governments or users. These and other issues must be addressed before wind energy will be used to provide a large portion of electricity on a utility grid.
More recently, there has been a large push by the United States and other nations to move to an integrated hydrogen economy in which hydrogen is used as a fuel in automobiles and even as a fuel for generating electricity. While hydrogen may be generated in a number of ways, a growing trend is to convert water by electrolysis to produce hydrogen. In this regard, an electrolyzer uses an electric current to separate water into hydrogen and oxygen. Many have suggested that renewable energy sources, such as wind, should be used to provide the electricity that in turn can be used to produce the hydrogen for use as a fuel. When a wind turbine is used to produce the hydrogen, the hydrogen can be used to drive a fuel cell or combination device which can convert hydrogen into electricity.
As with wind energy, there are a number of obstacles that must be overcome to facilitate adoption of hydrogen as a useful alternative to fossil fuels. For example, the production of electricity with fuel cells is relatively expensive when compared with other sources of electricity. Specifically, during the wind-electricity-hydrogen-electricity cycle proposed by many to address the intermittent nature of wind energy, a number of inefficiencies and losses occur in existing technologies such that the electricity produced by the fuel cell from hydrogen is much more expensive than can be obtained from other grid sources. In other words, the cost of electricity from the stored chemical energy in the form of hydrogen is higher than the initial electricity generated by the wind turbine, which is already generally higher than other grid sources.
Storage and distribution of the hydrogen creates another challenge. In some cases, generated hydrogen is transmitted as it is produced via a pipeline, but this involves pumping or compression costs to raise the pressure of generated hydrogen to that of the pipeline. In other cases, a separate pressure vessel is positioned near the electrolyzer to store the hydrogen for later distribution or use by a fuel cell. The compression and storage costs of the hydrogen can be significant and must be considered when analyzing hydrogen production and storage concepts. For example, the cost of pressure vessels for storing hydrogen for driving a fuel cell must be considered when determining the cost of associated with generating electricity from the stored or reserve energy for a wind farm.
Hence, there remains a need for improved methods and systems for generating electricity from wind that addresses the issues of cost, reliability, and dispatchability. Also, there is a need for improved methods and apparatus for generating, storing, and distributing hydrogen. Preferably, such methods would build upon existing wind and hydrogen technology while reducing costs and improving efficiencies.